Antenna duplexer

Abstract: Resonator holes (2a to 2d) are formed extending one to the other of a pair of opposing end surfaces of a dielectric block (1), and inner conductors (3a to 3d) are formed on inner peripheral surfaces of resonator holes (2a to 2d) respectively. On an outer surface of dielectric block (1), a pair of input/output electrodes (5a, 5b) and one antennal electrode (6) are formed, and expect these regions, an outer conductor (4) is formed. By the coupling of two resonators corresponding to the resonator holes (2a, 2b), a transmitting filter is provided, and by two resonators corresponding to resonator holes (2c, 2d), a receiving filter is formed.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to an antenna duplexer. More specifically, the present invention relates to an antenna duplexer used for mobile communication equipments such as automobile telephone and portable telephone. Description of the Background Art Fig. 1 is an equivalent circuit diagram of an antenna duplexer serving both as an antenna for a transmitter and an antenna for a receiver. Referring to Fig. 1, the antenna duplexer includes three terminals for input and output, that is, transmitting terminal TX, receiving terminal RX and an antenna terminal ANT. Resonators R1 and R2 are for the transmitter, and resonators R3 and R4 are for the receiver. One end of each of these resonators R1 to R4 is grounded. The other end of resonator R1 is connected to transmitting terminal TX through an external coupling capacitance Ce1, and the other end of resonator R2 is connected to antenna terminal ANT through external coupling capacitance Ce2. The other end of resonator R3 is also connected to antenna terminal ANT through external coupling capacitance Ce3, and the other end of resonator R4 is connected to receiving terminal RX through an external coupling capacitance Ce4. Fig. 2 is a perspective view showing a specific example of the antenna duplexer shown in Fig. 1. Referring to Fig. 2, the antenna duplexer includes two dielectric filters la and lb, and a coupling board 20. Each of the dielectric filters 1a and 1b consists of two stages of resonators. More specifically, dielectric filter la includes an approximately rectangular dielectric block 10a which includes two resonator holes 21a and 22a extending from an apertured surface 11a to the other surface 12a opposing to the apertured surface 11a, and inner conductors 31a and 32a formed on inner peripheral surfaces of resonator holes 21a and 22a, respectively. At corner portions extending from both side surfaces to the bottom surface of dielectric block 1a, a pair of input/output electrodes 5la and 52a are formed. On the outer peripheral surface except the regions on which input/output electrodes 51a and 52a are formed, an outer conductor 4a is provided. The inner conductors 31a and 32a are not provided at end portions of resonator holes 21a and 22a on the side of the apertured surface (hereinafter referred to as open end surface) 11a, and therefore on this side 11a, inner conductors 31a and 32a are isolated from external conductor 4a (not connected). On the other surface (hereinafter referred to as short-circuited surface) 12a opposing to the open end surface 11a, the resonator holes 21a and 22a are connected with the external conductor 4a (short-circuited). The other dielectric filter 1b is formed similarly as the above described dielectric filter 1a. Namely, it includes a dielectric block 10b, resonator holes 21b and 22b, inner conductors 31b and 32b, an outer conductor 4b, input and output electrodes 51b and 52b, an open end surface 11b and a short-circuited end surface 12b. Meanwhile, the coupling board 20 is for coupling two dielectric filters 1a and 1b placed parallel to each other, and it includes input/output electrodes 201 and 202 and an antenna electrode 203 formed on the surface thereof. Input/output electrode 201 corresponds to the input/output electrode 51a of one dielectric filter 1a, input/output electrode 202 corresponds to the input/output electrode 52b of the other dielectric filter 1b, and antenna electrode 203 corresponds to input/output electrodes 52a and 51b of the dielectric filters 1a and 1b. On the entire surface of coupling board 20 except the regions where input/output electrodes 201 and 202 and antenna electrode 203 are formed, a ground conductor 204 is formed. The dielectric filters 1a and 1b structured as described above constitute filters each having two stages of resonators, by the coupling of the resonators formed in resonator holes 21a and 22a, and 21b and 22b, respectively. Here, resonators R1 and R2 shown in Fig. 1 represent resonators formed by resonator holes 21a and 22a of dielectric filter 1a, while resonators R3 and R4 represent resonators formed by resonator holes 21b and 22b of dielectric filter 1b. The external coupling capacitance Cel between resonator R1 and transmitting terminal TX, the external coupling capacitance Ce4 between resonator R4 and receiving terminal RX and external coupling capacitances Ce2 and Ce3 between resonators R2 and R3 and antenna terminal ANT respectively, are provided by interelectrode capacitances formed between input/output electrodes 51a, 52a, 51b, 52b and corresponding inner conductors 31a, 32a, 31b, and 32b of the dielectric filters 1a, and 1b. However, in the conventional antenna duplexer shown in Fig. 2, two dielectric filters 1a and 1b formed by two dielectric blocks 10a and 10b as well as a coupling board 20 for connecting, fixing and mounting the filters, are necessary for forming the antenna duplexer. This requires in large number of parts and steps of assembly and soldering of these components. This impedes reduction in size, and increases the cost of components, the number of manufacturing steps and the cost of manufacturing. Another known example of the conventional antenna duplexer includes a number of dielectric resonators each having one resonator hole formed in one dielectric block, arranged parallel to each other. In such an example, external component such as capacitor element is necessary in addition to the coupling board, which results in larger number of parts. US-A-5250916 describes a filter duplexer for a radio transceiver. A first filter portion of the duplexer filter includes resonators of a first geometric configuration, and a second filter circuit portion of the duplexer filter comprises resonators of a second geometric configuration. EP-A-0508734 describes a filter which can be manufactured in a single ceramic block. The filter has on one side surface strip-like areas of electrically conducting material located in the area between the resonators of the filter. The dimensions of the strip-like areas are selected so that they substantially cancel the electric and magnetic field between the resonators. SUMMARY OF THE INVENTION Therefore, it is desirable to provide a surface mountable antenna duplexer which can reduce the number of parts, reduce the steps of manufacturing, which is inexpensive and allows reduction in size. According to one aspect of the present invention, there is provided an antenna duplexer, comprising: a dielectric block having a pair of opposing end surfaces; a plurality of resonator holes formed extending from one to the other of the pair of end surfaces of said dielectric block; inner conductors formed on inner peripheral surfaces of said resonator holes; an outer conductor formed on an outer peripheral surface of said dielectric block; and a common electrode and a pair of input/output electrodes electrically coupled to said inner conductors, formed at portions of said outer conductor; wherein said plurality of resonator holes and said plurality of inner conductors provides a portion serving as a transmitting filter and a portion serving as a receiving filter formed in said dielectric block; characterised in that the antenna duplexer further comprises a through hole having an inner conductor which is connected to said outer conductor and is formed between the transmitting filter portion and the receiving filter portion, parallel to said plurality of resonator holes, said through hole being arranged to improve isolation between said transmitting filter portion and said receiving filter portion. Therefore, two dielectric filters, that is, a transmitting filter and a receiving filter, are formed in one dieletric block, input/output electrodes and a common electrode for connection with external circuit are formed on an outer surface of the dielectric block, and the two filters are coupled by the common electrode, so that an antenna duplexer can be formed only by one dielectric block. More preferably, between the portion serving as the transmitting filter and the portion serving as the receiving filter, a through hole having an inner conductor conducted to outer conductor is formed parallel to the plurality of resonator holes. By the provision of this through hole with an inner conductor, isolation between the transmitting filter and receiving filter can be improved. More preferably, by electrically connecting the inner conductor, which is connected to the outer conductor at its other end, of the through hole with the common electrode, an inductance can be formed between the common terminal and the ground for absorbing reflected phase of the transmitting filter and the receiving filter. According to another aspect of the present invention, there is provided an antenna duplexer for use in mobile communications, said antenna duplexer comprising: a single dielectric body, a plurality of resonator holes formed within said dielectric body; and a plurality of electrodes provided as terminals for said duplexer; wherein said plurality of resonator holes and said plurality of electrodes are arranged into portions providing at least one transmitting filter and at least one receiving filter, characterised in that a through hole having an inner conductor is provided between said at least one transmitting and said at least one receiving filter, said through hole being arranged to improve isolation between said at least one transmitting filter and said at least one receiving filter. The above and further features of the present invention are set out with particularity in the appended claims and, together with the advantages thereof, should become clear from consideration of the following detailed description given with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an equivalent circuit diagram of a conventional antenna duplexer. Fig. 2 is a perspective view of a conventional antenna duplexer. Fig. 3 is a perspective view of another conventional duplexer. Fig. 4 is a perspective view of an embodiment of the present invention. Fig. 5 is a perspective view of another embodiment of the present invention. Fig. 6 is an equivalent circuit diagram of the embodiment shown in Fig. 5. DETAILED DESCRIPTION OF THE EMBODIMENTS Fig. 3 is a perspective view of an antenna duplexer. Referring to Fig. 3, the antenna duplexer includes an approximately rectangular parallelepiped dielectric block 1. Four resonator holes 2a, 2b, 2c and 2d are formed extending from one to the other of a pair of opposing end surfaces of the dielectric block 1. Inner conductors 3a, 3b, 3c and 3d are formed on inner peripheral surfaces of resonators 2a to 2d, respectively. On an outer peripheral surface of dielectric block 1, an outer conductor 4 is formed except at regions where a pair of input/output electrodes 5a and 5b and one antenna electrode 6 are formed. A pair of input/output electrodes 5a and 5b is formed extending from the surface of dielectric block 1 which will be surface-mounted onto the substrate (upper surface of Fig. 3) to one and the other side surfaces of dielectric block 1, respectively, near the open end surface 13a. Antenna electrode 6 is formed at the side surface of dielectric block 1 near the open end surface 13a, between the input/output electrodes 5a and 5b. Each one end of inner conductors 3a to 3d are isolated from (not connected with) outer conductor 4 which slightly comes into the resonator holes 2a to 2d, since there are portions not provided with any conductor near the open end surface 13a (in other words, the surface of the dielectric block material is exposed in a ring-shape near the end surface 13a around the resonator holes 2a to 2d), while the other ends of the inner conductors 3a to 3d are connected (short-circuited) with outer conductor 4 at the short-circuited end surface 13b opposite to the open end surface 13a. Input/output electrodes 5a, 5b and antenna electrode 6 are isolated from outer conductor 4, as there is a non-conductive portion around each of these electrodes. In the antenna duplexer structure as described above, between inner conductors 3a and 3d of resonator holes 2a and 2d and input/output electrodes 5a and 5b opposing to the resonator holes 2a and 2d, and between inner conductors 3b and 3c of resonator holes 2b and 2c and antenna electrode 6, there are formed external coupling capacitances Ce1 to Ce4, as schematically shown in Fig. 3. By the coupling of two resonators corresponding to resonator holes 2a and 2b, a transmitting filter is formed. By the two resonators corresponding to resonator holes 2c and 2d, a receiving filter is formed. The transmitting filter and the receiving filter are coupled sharing the antenna electrode 6, and thus an integrated antenna duplexer having three terminals for input/output, that is, antenna electrode 6 and a pair of input/output electrodes 5a and 5b is provided, which corresponds to the equivalent circuit shown in Fig. 1 of the prior art. Now, the resonators R1 and R2 shown in Fig. 1 correspond to the resonators formed by resonator holes 2a and 2b, while resonators R3 and R4 correspond to the resonators formed by resonator holes 2c and 2d. The external coupling capacitances Ce1 and Ce4 between resonator R1 and transmitting terminal TX and resonator R4 and receiving terminal RX are obtained by interelectrode capacitances formed between input/output electrodes 5a and 5b and inner conductors 3a and 3d of resonator holes 2a and 2d corresponding thereto, while external coupling capacitances Ce2 and Ce3 between resonators R2 and R3 and antenna terminal ANT are obtained by interelectrode capacitances formed between the antenna electrode 6 and inner conductors 3b and 3c of resonator holes 2b and 2c, respectively. When the antenna duplexer is to be mounted on a substrate, the surface on which input/output electrodes 5a and 5b and antenna electrode 6 are formed (upper surface of Fig. 3) serves as the bottom surface which is mounted on the substrate. As described above, since transmitting and receiving two dielectric filters are formed in one dielectric block, and input/output electrodes 5a and 5b and an antenna electrode 6 for connection to an external circuit are formed on an outer surface of dielectric block 1 with the two filters coupled by the antenna electrode, an antenna duplexer can be implemented by only one dielectric block 1. Therefore, the number of components can be reduced, the number of manufacturing steps can be decreased and the cost can be reduced. Fig. 4 is a perspective view showing an embodiment of the present invention. The embodiment shown in Fig. 4 includes a through hole 7 formed between the transmitting and receiving filters of the antenna duplexer of the embodiment shown in Fig. 3, that is, between resonator holes 2b and 2c, parallel to the holes 2b and 2c. An inner conductor 3e is formed on the inner peripheral surface of through hole 7, and the conductor is connected (short-circuited) with the outer conductor 4 at both end surfaces, that is, the open end surface 13a and the short-circuited end surface 13b. Other structures are the same as those of Fig. 3. In the embodiment shown in Fig. 4, by the inner conductor 3e of the through hole 7 connected to outer conductor 4, the transmitting filter and the receiving filter are shielded, and therefore isolation between the filters can be improved. Fig. 5 is a perspective view showing still another embodiment of the present invention, and Fig. 6 is an equivalent circuit diagram of the embodiment shown in Fig. 5. In this embodiment shown in Fig. 5, a through hole 8 is formed between the transmitting filter and the receiving filter of the antenna duplexer shown in Fig. 3, that is, between resonators 2b and 2c, parallel to the resonators 2b and 2c. An inner conductor 3f is formed on the inner peripheral surface of the through hole 8, and a through hole 9 is further provided which connects (conducts) inner conductor 3f to antenna electrode 6. In the similar manner as conductors 3a to 3d of resonator holes 2a to 2d, one end of inner conductor 3f formed on the inner peripheral surface of through hole 8 is isolated from outer conductor 4 as there is a portion not provided with any conductor near the open end surface 13a, while it is conducted with outer conductor 4 at the short-circuited end surface 13b. Other structures are the same as those of Fig. 3. In the antenna duplexer shown in Fig. 5, an inductance L such as shown in Fig. 6 is formed between antenna electrode 6 and outer conductor 4, by the inner conductor 3f of the through hole 8 connected to antenna electrode 6 by means of through hole 9. The inductance L is capable of absorbing or annulling reflected phase or susceptance of the transmitting filter and the receiving filter between the antenna terminal ANT and the ground. As described above, in the antenna duplexer of each of the embodiments, the transmitting filter and the receiving filter are provided by one dielectric block 1, and input/output electrodes 5a and 5b and antenna electrode 6 for connection to an outer circuit are formed on an outer surface of dielectric block 1, and therefore a component such as coupling board used in the conventional antenna duplexer becomes unnecessary. By providing a through hole having an inner conductor formed between the transmitting and receiving filters as in the second and third embodiments, isolation between the transmitting and receiving filters can be improved. Further, an antenna duplexer having an inductance for absorbing reflected phase of transmitting and receiving filters inserted between antenna terminal ANT and the ground can be provided by one dielectric block. The shape, location and the like of the input/output electrodes 5a, 5b and antenna electrode 6 of respective embodiments are not limited to those disclosed, and the shape, dimension, positions may be arbitrarily changed so as to change the capacitance values, and to provide aimed filter characteristics. Isolation between the outer conductor and the inner conductor on the side of the open end surface 13a is implemented by not providing the inner conductor near the open end surface 13a in the embodiments described above. However, it is not limited to this, and a non-conducting portion may be provided on the open end surface 13a. Namely, one end in the axial direction of the inner conductor may reach the open end surface 13a. Alternatively, the outer conductor may not be provided at all on the open end surfaces 13a. Though a resonator hole has a constant diameter in the embodiments above, the diameter of the resonator hole may be changed midway, and a coupling groove for changing the degree of coupling between each of the resonators may be provided at the top and bottom surfaces of dielectric block 1, or a coupling hole for changing the degree of coupling between each of the resonators may be provided between the resonators. Though an antenna duplexer including a transmitting filter consisting of two stages of resonators and a receiving filter consisting of two stages of resonators has been described in the embodiments above, each filter may be constituted by three or more stages of resonators including three or more resonator holes.

Claims: An antenna duplexer, comprising: a dielectric block (1) having a pair of opposing end surfaces (13a, 13b); a plurality of resonator holes (2a to 2d) formed extending from one to the other of the pair of end surfaces (13a, 13b) of said dielectric block (1); inner conductors (3a to 3d) formed on inner peripheral surfaces of said resonator holes (2a to 2d); an outer conductor (4) formed on an outer peripheral surface of said dielectric block (1); and a common electrode (6) and a pair of input/output electrodes (5a, 5b) electrically coupled to said inner conductors (3a to 3d), formed at portions of said outer conductor (4); wherein said plurality of resonator holes (2a to 2d) and said plurality of inner conductors (3a to 3d) provide a portion (R 1 , R 2 ) serving as a transmitting filter and a portion (R 3 , R 4 ) serving as a receiving filter formed in said dielectric block (1); characterised in that the antenna duplexer further comprises a through hole (7) having an inner conductor (3e) which is connected to said outer conductor (4) and is formed between the transmitting filter portion (R 1 , R 2 ) and the receiving filter portion (R 3 , R 4 ), parallel to said plurality of resonator holes (2a to 2d), said through hole (7) being arranged to improve isolation between said transmitting filter portion (R 1 , R 2 ) and said receiving filter portion (R 3 , R 4 ). The antenna duplexer according to claim 1, further comprising: a connecting member (9) for electrically connecting one end of the inner conductor (3f) of said through hole (8) with said common electrode (6); wherein the inner conductor (3f) of said through hole (8) is connected to said outer conductor (4) at the other end (Figure 5). The antenna duplexer according to claim 2, wherein said connecting member (9) and said through hole (8) are arranged to form an inductor (L) (Figure 5). The antenna duplexer according to any preceding claim, wherein said pair of input/output electrodes (5a, 5b) include electrodes provided at corners formed of side surfaces and a plane between one and the other of said pair of end surfaces (13a, 13b), and said common electrode (6) includes an electrode formed on said plane between said pair of input/output electrodes (5a, 5b). An antenna duplexer for use in mobile communications, said antenna duplexer comprising: a single dielectric body (1), a plurality of resonator holes (2a to 2d) formed within said dielectric body (1); and a plurality of electrodes (5a, 5b, 6) provided as terminals for said duplexer; wherein said plurality of resonator holes (2a to 2d) and said plurality of electrodes (5a, 5b, 6) are arranged into portions providing at least one transmitting filter (R 1 , R 2 ) and at least one receiving filter (R 3 , R 4 ), characterised in that a through hole (7) having an inner conductor (3e) is provided between said at least one transmitting filter (R 1 , R 2 ) and said at least one receiving filter (R 3 , R 4 ), said through hole (7) being arranged to improve isolation between said at least one transmitting filter (R 1 , R 2 ) and said at least one receiving filter (R 3 , R 4 ).

Inventors: KATO HIDEYUKI, TADA HITOSHI, KATO, HIDEYUKI, TADA, HITOSHI, KATO, HIDEYUKI, MURATA MANUF.CO.,LTD., TADA, HITOSHI, MURATA MANUF.CO.,LTD.
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1994
Main classification: H01P1
IPC codes: H01P1, H01P5